More stringent environmental regulations require novel approaches to minimize NOx emissions from major sources, such as on-road and off-road vehicles. Current logistic fuels, such as diesel, kerosene, JP-8, gasoline, and natural gas are the preferred choice as reductants for NOx reduction aftertreatment systems, such as hydrocarbon selective catalytic reduction (HC-SCR) and lean NOx traps (LNT). This is primarily due to the fact that such fuels are already carried on-board a vehicle as the combustion fuel for the engine and, therefore no special secondary treatment is required. However, the direct use of these fuels as reducing agents in catalytic aftertreatment systems is known. Hydrocarbon species which make up the fuel are not the actual reductant used in NOx reduction chemistry. Instead, most catalyst formulations contain one or more “promoters”, which are typically made up from precious metals or base metal oxides, whose function is to “convert” fuel hydrocarbons into partially oxidized species like alcohols, aldehydes or ketones. It is these oxygenates that are active in the chemical reduction of NOx on the surface of most lean-NOx catalysts.
Currently, some of the most active reductants for HC-SCR are aldehydes and alcohols such as methanol, ethanol, acetaldehyde, and formaldehyde. On-board production of these reductants would allow for better performance of the catalyst system to meet the more stringent environmental regulations for NOx emissions. The enhanced performance of aldehydes and alcohols over traditional hydrocarbons (propylene) is based on the broadening of the active temperature window, higher selectivity, and higher overall activity for reduction of NOx.
Accordingly, the ability to transform fuel hydrocarbons into oxygenated species in a manner that allows for high activity and control over the selectivity would be a break-through in the aftertreatment industry. The invention described herein provides for a method to produce specific oxygenates from diesel, natural gas, JP-8, and other hydrocarbon fuels.